Adjustment instruments for an exterior mirror unit are generally known and are widely used on vehicles, for example, automobiles. Such an adjustment instrument usually comprises a housing which is pivotably adjustable between a park position, a drive position and a fold-over position. In the park position the exterior mirror unit extends substantially along the vehicle, with a mirror side facing the vehicle. In the drive position the exterior mirror unit is directed substantially transverse to the vehicle. In the fold-over position the exterior mirror unit extends substantially along the vehicle, with the mirror side facing away from the vehicle. For example in the event of an impact such as a collision, the exterior mirror unit can be moved to the fold-over position.
Adjusting the exterior mirror unit from the park position to the drive position and vice versa can be done electrically or manually. An electrically adjustable adjustment instrument is provided with an electrical drive in the housing which is couplable with a drive ring. Via the drive ring the housing can be pivoted around the base. Also in an electrically adjustable adjustment instrument, provision is made to allow the instrument to be manually adjusted between the park position and the drive position and/or fold-over position. A drawback of the known electrically adjustable adjustment instruments is that during manual adjustment the drive is subject to relatively large forces, which requires the drive to be made of relatively heavy and costly construction.
A further drawback of the known electrically adjustable adjustment instruments is that the position of the drive position is sometimes not well-defined so that the housing may start to vibrate during driving. Also, in that case the shape of the housing cannot properly align with the shape of the suspension point of the housing. This is not desirable for esthetic and aerodynamic reasons.
An object of the invention is to provide an electrically adjustable adjustment instrument that obviates at least one of the above-mentioned drawbacks.